FROM AROUND THE STATE
ISSUE 5 June 3 2004
Effect of Cool Wet Weather on Insect Pests:
Grasshoppers on Agricultural Crops
There have been a few reports of grasshoppers being numerous on field edges of canola and small grains in spite of the cool wet weather. Although some of the young grasshoppers have started to emerge in May, there are many eggs that have not hatched yet. Grasshoppers that hatched during the rainy periods are more susceptible to fungal diseases and drowning in heavy rains. With warmer, sunny weather forecasted for this week, grasshoppers should start emerging again. Field edges and ditches should be scouting for these tiny grasshoppers to determine the need for any treatments. There is abundant vegetation in the ditches, which should provide ample food sources for these hungry young grasshoppers. Fortunately, this could slow their movements into field edges of agricultural crops.
Crucifer flea beetles in Canola
High populations of Crucifer flea beetles were detected last summer in swathed fields in most of the canola growing regions of ND. High populations the previous year usually translate into high populations the following spring! Many have been wondering if flea beetle populations may have crashed or have been killed off by the cool wet weather conditions. The delayed emergence may have killed some of the overwintering flea beetles due to declining body fats, which are required to maintain their hibernating state. However, entomologists still expect most of the flea beetles to survive quite well, and to continue their spring emergence as soon as the warmer weather returns. For any early planted canola that been in the ground for 21-26 days and barely emerging or in the seedling stage, the residue of the insecticide-fungicide seed treatments (like Helix xtra and Prosper 400) is gone! It will NOT protect the small canola plants (less than 6-8 leaf stage) against flea beetles. A foliar insecticide spray will be needed on top of the canola seed treatments as flea beetle feeding activity increases in early June.
Remember, flea beetles can move very fast when weather conditions are warm (>60įF) with light winds, and can quickly defoliate a small canola seedling in large numbers. Capture and Warrior (both pyrethroids) are labeled as foliar sprays on canola and can be safely tank-mixed with the herbicides labeled in canola. A residual of 7-10 days can be expected from these pyrethroids.
Some reports of cutworm activity have come in. So, continue to watch your fields for any cut plants and dig up any cutworm larvae located under the cut plant. The wet soil conditions will cause them to feed close to the soil surface making them easy prey for other predators (sea gulls, ground beetles) and easier to kill with insecticides. Fungal diseases could also cause some mortality with cutworms. The cool conditions will slow their feeding activities and larval development. Cutworms are usually active into late June in ND. Remember, early detection is critical for effective cutworm control. Cutworm damage is often localized in certain areas of the field, and in some situations insecticide sprays can be targeted at those infested areas.
White Grubs in Pastures
There have been several reports of white grubs, C-shaped larvae, in pastures in NC Region (see photo on right). White grubs are significant pests in many agricultural systems including pastures. White grubs are larvae of the adult June beetles (Scarabaeidae: Phyllophaga spp.). Their life cycle varies from two to four years depending on the species, usually 3 years in ND. Adults emerge in spring and feed on foliage of broadleaf and coniferous trees and bushes during the first year. June beetles deposit eggs in spring in pastures or in grassy areas adjacent to fields. Egg hatch in three to four weeks into white grubs, which feed on the roots and organic matter. As soil temperature declines in fall, these grubs move deeper into the soil below the frost line until next spring. The larval feeding process is repeated two-three more years. The worst damage is usually caused during the second year, because larger grubs are present and actively feeding. When growth is complete, grubs pupate in an earthen cell. The adult remains in the cell until the following spring and then emerge to repeat the life cycle.
White grubs feed on decaying organic matter and roots from 1-4 inches below the soil surface, killing seedlings and sometimes older plants, and reducing drought tolerances. Grubs tunnel near the soil surface leaving trails of pulverized soil. Tunneling loosens the soil and creates a spongy layer about 2 inches deep in heavy infestations. Grazing cattle easily pull the plants growing in the pulverized soil. Weeds quickly colonize the bare patches created where grass has died or is pulled out. Birds, rodents, skunks, badgers, and other wildlife dig up and eat white grubs as a food source, often causing greater damage in the process. White grub infestations are usually patchy. Edges of terraces, sunny slopes, slopes down from barns, and cattle feeding sites are all likely to be infested.
Guidelines for White Grub Pest Management in Pastures:
Be sure you have white grubs. Scout pastures and hayfields for white grubs in late summer and early fall. By August, most June beetles will have hatched from their eggs. Check fields for signs of infestation, such as trails of pulverized soil and bare patches. Pay close attention to edges of terraces, sunny slopes, slopes down from barns, and cattle feeding sites. Check to see how many grubs are present. With a shovel, carefully dig 1 square foot area down to about 3-4 inches deep. Count the number of white grubs in the soil. Repeat this in at least 5 areas of the field.
Decide whether an insecticide is needed. Although there is no threshold established for white grubs in pastures in ND, other states have used 4 or more grubs per square foot as an insecticide threshold. White grub control is generally considered too expensive in low value grassland.
Be sure conditions are right for best control. In most years, the best time for grub control is August through September, before the June beetle grubs have caused extensive damage. Mow or closely graze pastures before spraying. It is important that the grubs come in contact with the insecticide. Make applications late in the day since grubs move to the surface during the evening. Applying the insecticide a few hours before a moderate rain may increase the efficacy of the application. Heavy infestations may require a second application 10 days to 2 weeks after the first application. Treatments during early spring will be too late to prevent most white grub damage and will probably give a lower percentage of control. Grubs are larger by this time and are harder to kill. Also, when temperatures are cool, control efficacy declines because grubs are less likely to come to the surface and come in contact with the insecticide.
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center
During the past week (May 26 to June 1), the south-central regionís rainfall ranged from 1.02 inches at Linton to 4.42 inches at Dazey as recorded at NDAWN (North Dakota Agricultural Weather Network) sites. Most of the area received 2 to 4 inches of rain, with grower reports of up to 7 inches.
The regionís cool-season crop and corn planting essentially is complete. Most spring wheat is at the 3- to 5-leaf stage and timely-planted corn is in the 1- to 3-leaf stage. Yield potential of small grain currently is excellent due to cool weather conditions present during the tillering stage and the ample soil moisture. The majority of soybean, dry bean and sunflower acres have been planted and remaining acreage should quickly be finished when soil conditions permit re-entry into fields. Also, farmers will be planting millet and warm-season forages.
POST herbicide spraying in small grain will continue with cooperative weather. Weed emergence and growth is accelerating with the recent rainfall and warmer air temperatures. Growers should be monitoring spring wheat for tan spot and consider early-season fungicide application with herbicides especially if wheat residue is present in the field and leafspot-susceptible varieties are grown. Other pest problems currently appear minimal.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center
Weather remains dry around much of southwest North Dakota. Greatest rainfall amount received at an NDAWN site south and west of the Missouri River for the week was at Watford City, which received 0.99 inches. Unfortunately, significant rainfall amounts stayed to the north and east. Both Dickinson and Mandan reported 0.12 inches of precipitation for the week while Bowman and Hettinger reported zero. Wind was plentiful during the Memorial Day weekend. Beach and Bowman had winds of 50 to 54 mph. Earlier in the week wind conditions over a two-day period permitted herbicide and early season fungicide applications.
Emergence of corn planted in tilled fields is uneven while in no-till fields corn emergence appears to be even. The same holds true with late seeded cereal grains.
Winter wheat and winter rye have been developing under dry conditions so the crop is relatively short. Dissected winter wheat heads from one field in Hettinger County indicate only about 10 to 12 spikelets per head. Eric Eriksmoen, Agronomist for the Hettinger Research Extension Center indicated canola stands are only about Ĺ of normal due to dry weather during establishment and freezing temperatures in mid-May. Canola and mustard are beginning to bloom.
The dry cold weather has affected pastures. Grass is short and producers are looking for pasture and hay.
Area Extension Agronomist
Dickinson Research Extension Center